Strainburst is the most frequently encountered rockburst in underground mines. Conventional method to support strainburst-prone grounds is to install rock reinforcement system using rebar and mesh first and then install yielding support system using dynamic rockbolts at a later stage. This two-stage rock support installation process is not safe and effective because it can adversely impact worker's safety and mine production schedule. Two new dynamic rockbolts, which are called Superbolts, are developed for rapid rock support in burst-prone grounds. Laboratory testing confirmed that the new rockbolts have superb capacities to achieve the goal of reinforcing and holding rock masses at the same time. Detailed test results of the MCB-Superbolts are presented in this paper. The new rockbolts are quick to install and can be used in a one-pass rock support system to facilitate safe and rapid drift development in underground mines.
Failure of drifts in underground mines may be stress driven or structurally controlled. Several rock mass failure modes such as fall of ground due to wedge failure, squeezing and rockbursting have been identified in underground mine construction. In deep hard rock mines, stress-driven failure in the form of rockburst poses a great danger to workers and construction equipment. A rockburst is defined as damage to an excavation that occurs in a sudden and violent manner and is associated with a seismic event (Kaiser et al., 1996). Fault-slip burst, pillar burst and strainburst are three rockburst types that occur in underground excavations and constructions. Among them, strainbursts are the mostly commonly encountered rockbursts.
Rockburst damages near excavations can be in the forms of static stress fracturing or strainbursting due to tangential straining, shakedown due to acceleration forces from a remote seismic event, and rock ejection by momentum or energy transfer from a remote seismic source or due to high bulking deformation rates during strainburst (Kaiser et al., 1996; Cai & Kaiser, 2018). Sudden stress fracturing of rock leads to a disintegration of the rock mass and this is associated with rock mass bulking in the radial direction of tunnels. This inward movement can be described by a bulking factor (Kaiser et al., 1996). Seismically induced rockfalls, which occur frequently at intersections where the span is large and the confinement of the roof rock is low, are caused by seismic waves from relatively large and remote seismic events that shake the entire volume of a potentially unstable mass of rock. Rock ejection can be caused by strainbursts, by a remote seismic event through dynamic energy or momentum transfer, or by a combination of both. Rockburst damage severity can be roughly classified into minor, moderate, and major or severe levels based on the volume of failed or displaced rock, the degree of support damage, and the violence of the energy release in terms of impact or ejection velocity. Detailed descriptions of the severity levels can be found in Kaiser et al. (1996).
